Boris Johnson is on course to win the London mayoral elections, although with a narrower lead than previously predicted, according to a poll published today.

The final YouGov poll for the Evening Standard gave the Conservative candidate a lead of seven points on first-preference votes over the mayor, Ken Livingstone, down from an 11-point lead earlier in the week.

It said 43% of voters were going to back Johnson with their first vote, and 36% supported Livingstone. After the re-allocation of second-preference votes, it predicted a Johnson victory by 53% to 47%.

However, YouGov has consistently given Johnson higher leads than other polling organisations and many analysts believe the race is too close to call. A poll for Ipsos Mori last week put Livingstone 4% ahead and another for MRUK put him 2% in front.

Livingstone, who was predicting yesterday that he would win by 52% to 48%, voted early near his home in Cricklewood, north London.

His campaign received a boost when Simon Hughes, the Liberal Democrats' former mayoral candidate, gave a strong hint that Lib Dem supporters should back Labour's Livingstone with their second-preference votes.

"Brian Paddick [the Lib Dem candidate for mayor] knows exactly what is needed to make our capital respectful, prosperous and safe," said Hughes, the MP for North Southwark and Bermondsey.

"I shall enthusiastically give Brian Paddick my first vote and call on all Londoners to do the same. I hope all voters will use the same test to decide their second vote as well.

"Nobody who has not served London and worked for London deserves to have the votes of Londoners or the top political job in London in the future."

Johnson was in upbeat mood when he cast his vote. "If you look at the reaction we've been getting on the streets and people's desires for new solutions, you'd have to be optimistic," he said.

Paddick cast his vote this morning at his local polling station in Vauxhall.